Apparatus for attaching radiopaque markers to a stent

ABSTRACT

A mandrel for supporting a stent and rollers for pressing a radiopaque marker into a stent are disclosed. The mandrel can have a forward portion for carrying the stent and a rear portion for urging the stent forward portion into a gap between the rollers. The mandrel may be pushed or pulled into the gap, which is sized to allow the rollers to press the marker into engagement with the stent. Prior to moving the mandrel into the gap, the marker may be placed on a surface of the stent or partially inside a recess in the stent. Several markers can be efficiently and uniformly pressed onto the stent by moving the mandrel into the gap in one continuous movement in an axial or lateral direction. Markers can also be pressed onto the stent by placing the stent in the gap and rotating the stent about its central axis.

This application is a continuation of U.S. application Ser. No.13/399,898 filed on Feb. 17, 2012, which is a divisional application ofU.S. application Ser. No. 12/881,968 filed on Sep. 14, 2010, now U.S.Pat. No. 8,127,422, which is a divisional application of U.S.application Ser. No. 11/771,974 filed on Jun. 29, 2007, now abandoned,which claims the benefit of U.S. Provisional Application No. 60/830,201filed on Jul. 11, 2006, the entire contents of which applications areincorporated by reference for all purposes.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to implantable medical devices, such asstents, and, more particularly, to attaching radiopaque markers topolymeric stents.

2. Description of the State of the Art

Expandable endoprostheses are adapted to be implanted in a bodily lumen.An “endoprosthesis” corresponds to an artificial device that is placedinside the body. A “lumen” refers to a cavity of a tubular organ such asa blood vessel. A stent is an example of such an endoprosthesis. Stentsare generally cylindrically shaped devices, which function to hold openand sometimes expand a segment of a blood vessel or other anatomicallumen such as urinary tracts and bile ducts. Stents are often used inthe treatment of atherosclerotic stenosis in blood vessels. “Stenosis”refers to a narrowing or constriction of the diameter of a bodilypassage or orifice. In such treatments, stents reinforce blood vesselsand prevent restenosis following angioplasty in the vascular system.“Restenosis” refers to the reoccurrence of stenosis in a blood vessel orheart valve after it has been treated (as by balloon angioplasty,stenting, or valvuloplasty) with apparent success.

The structure of stents is typically composed of scaffolding thatincludes a pattern or network of interconnecting structural elements orstruts. The scaffolding can be formed from wires, tubes, or sheets ofmaterial rolled into a cylindrical shape. In addition, a medicated stentmay be fabricated by coating the surface of either a metallic orpolymeric scaffolding with a polymeric carrier. The polymericscaffolding may also serve as a carrier of an active agent or drug.

The first step in treatment of a diseased site with a stent is locatinga region that may require treatment such as a suspected lesion in avessel, typically by obtaining an x-ray image of the vessel. To obtainan image, a contrast agent, which contains a radiopaque substance suchas iodine is injected into a vessel. “Radiopaque” refers to the abilityof a substance to absorb x-rays. The x-ray image depicts the lumen ofthe vessel from which a physician can identify a potential treatmentregion. The treatment then involves both delivery and deployment of thestent. “Delivery” refers to introducing and transporting the stentthrough a bodily lumen to a region in a vessel that requires treatment.“Deployment” corresponds to the expanding of the stent within the lumenat the treatment region. Delivery and deployment of a stent areaccomplished by positioning the stent about one end of a catheter,inserting the end of the catheter through the skin into a bodily lumen,advancing the catheter in the bodily lumen to a desired treatmentlocation, expanding the stent at the treatment location, and removingthe catheter from the lumen. In the case of a balloon expandable stent,the stent is mounted about a balloon disposed on the catheter. Mountingthe stent typically involves compressing or crimping the stent onto theballoon. The stent is then expanded by inflating the balloon. Theballoon may then be deflated and the catheter withdrawn. In the case ofa self-expanding stent, the stent may be secured to the catheter via aretractable sheath or a sock. When the stent is in a desired bodilylocation, the sheath may be withdrawn allowing the stent to self-expand.

The stent must be able to simultaneously satisfy a number of mechanicalrequirements. First, the stent must be capable of withstanding thestructural loads, namely radial compressive forces, imposed on the stentas it supports the walls of a vessel lumen. In addition to havingadequate radial strength or more accurately, hoop strength, the stentshould be longitudinally flexible to allow it to be maneuvered through atortuous vascular path and to enable it to conform to a deployment sitethat may not be linear or may be subject to flexure. The material fromwhich the stent is constructed must allow the stent to undergoexpansion, which typically requires substantial deformation of localizedportions of the stent structure. Once expanded, the stent must maintainits size and shape throughout its service life despite the variousforces that may come to bear thereon, including the cyclic loadinginduced by the beating heart. Finally, the stent must be biocompatibleso as not to trigger any adverse vascular responses.

In addition to meeting the mechanical requirements described above, itis desirable for a stent to be radiopaque, or fluoroscopically visibleunder x-rays. Accurate stent placement is facilitated by real timevisualization of the delivery of a stent. A cardiologist orinterventional radiologist can track the delivery catheter through thepatient's vasculature and precisely place the stent at the site of alesion. This is typically accomplished by fluoroscopy or similar x-rayvisualization procedures. For a stent to be fluoroscopically visible itmust be more absorptive of x-rays than the surrounding tissue.Radiopaque materials in a stent may allow for its direct visualization.

In many treatment applications, the presence of a stent in a body may benecessary for a limited period of time until its intended function of,for example, maintaining vascular patency and/or drug delivery isaccomplished. Therefore, stents fabricated from biodegradable,bioabsorbable, and/or bioerodable materials may be configured to meetthis additional clinical requirement since they may be designed tocompletely erode after the clinical need for them has ended. Stentsfabricated from biodegradable polymers are particularly promising, inpart because they may be designed to completely erode within a desiredtime frame.

However, a significant shortcoming of biodegradable polymers (andpolymers generally composed of carbon, hydrogen, oxygen, and nitrogen)is that they are radiolucent with no radiopacity. Biodegradable polymerstend to have x-ray absorption similar to body tissue.

One way of addressing this problem is to attach radiopaque markers tostructural elements of the stent. A radiopaque marker can be disposedwithin a structural element in such a way that the marker is secured tothe structural element. However, the use of stent markers on polymericstents entails a number of challenges. One challenge relates to thedifficulty of insertion of markers.

Another challenge pertains to the fact that some regions of polymericstruts tend to undergo significant deformation or strain during crimpingand expansion. In particular, such changes are due to plasticdeformation of polymers. Thus, during stent deployment, the portion of astent containing an element may crack or stretch as stress is beingapplied to the expanding stent. As a result, the marker may becomedislodged.

Attachment of radiopaque markers to stents usually requires asignificant amount of time to perform with reliability and uniformity.The amount of time required is increased when several markers must beattached at different locations on the stent. Also,conventionally-placed markers may project inward from the luminalsurface of the stent to such a degree that blood flow is disrupted, orproject outward from the abluminal surface of the stent to such a degreethat the walls of the blood vessel are traumatized.

Accordingly there is a need to for an apparatus and method of easilyattaching radiopaque markers on stents. There is also a need for anapparatus and method of attaching radiopaque markers on stents such thatthe marker is retained in the stent during deformation of the stentsduring subsequent stent crimping and expansion. There is a further needfor an apparatus and method of attaching a plurality of radiopaquemarkers to a stent with greater efficiency and uniformity. Also, thereis a need to attach radiopaque markers such that the radiopaque markersdo not overly protrude from the stent. The present invention satisfiesthese and other needs.

SUMMARY OF THE INVENTION

Various embodiments of the present invention include an apparatus forattaching a radiopaque marker onto a stent, comprising: a cylindricalmandrel including a forward portion and a rear portion, the forwardportion for supporting a stent; and rollers spaced apart by a gap thatis greater than or equal to an outer diameter of the rear portion of themandrel, wherein the rollers are oriented to allow each of the rollersto rotate about a rotational axis that is parallel to a longitudinalaxis of the mandrel, wherein the mandrel and rollers are movable inrelation to each other so that the mandrel passes into and through thegap.

Further embodiments of the present invention include an apparatus forattaching a radiopaque marker onto a stent, comprising: a cylindricalmandrel including a forward portion and a rear portion, the forwardportion for supporting a stent; and rollers spaced apart by a gap thatis greater than or equal to an outer diameter of the rear portion of themandrel, wherein the rollers are oriented to allow each of the rollersto rotate about a rotational axis that is parallel to a longitudinalaxis of the mandrel, wherein the mandrel and rollers are movable inrelation to each other, and wherein the mandrel is secured againstrotation.

The features and advantages of the invention will be more readilyunderstood from the following detailed description which should be readin conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a cylindrically-shaped stent.

FIG. 2 is a plan view showing a flattened stent pattern with depots forreceiving radiopaque markers.

FIG. 3 is a perspective view of a portion of a stent, showing a depotfor receiving a radiopaque marker.

FIG. 4 is a perspective view of the stent of FIG. 3, showing a sphericalradiopaque marker disposed over the depot.

FIG. 5 is a side view showing a stent with two radiopaque markersdisposed over openings in the stent.

FIG. 6 is an end view showing the stent and one of the markers of FIG.5.

FIG. 7 is a side view showing a mandrel for carrying a stent, themandrel having a forward portion and a rear portion.

FIG. 8 is a side view of an apparatus for attaching radiopaque markersonto a stent, showing the mandrel of FIG. 7 carrying the stent of FIG.5, and showing rollers having a rotational axis substantiallyperpendicular to the central axis of the stent, and the forward portionof the mandrel placed in a gap between the rollers.

FIG. 9 is a side view of the apparatus of FIG. 8 showing the mandrel andstent having been moved axially through the gap between the rollers andshowing the markers pressed into engagement with the stent.

FIG. 10 is a perspective view of a portion of the stent of FIG. 5,showing one of the radiopaque markers pressed into engagement with thestent after having passed through the gap between the rollers.

FIG. 11 is a side view of a marker attachment apparatus, showing a stentmounted on a mandrel and rollers adjacent the stent and mandrel, therollers having a rotational axis substantially parallel to the centralaxis of the stent such that a marker and the stent are pressed intoengagement with each other when the stent is moved laterally through agap between the rollers.

FIG. 12 is a side view of a marker attachment apparatus, showing a stentmounted on a mandrel and rollers adjacent the stent and mandrel, therollers having a rotational axis substantially parallel to the centralaxis of the stent such that a marker and the stent are pressed intoengagement with each other when the stent is placed between a gapbetween the rollers and rotated about its central axis.

DETAILED DESCRIPTION OF THE INVENTION

The present invention may be applied to stents and, more generally,implantable medical devices such as, but is not limited to,self-expandable stents, balloon-expandable stents, stent-grafts,vascular grafts, cerebrospinal fluid shunts, pacemaker leads, closuredevices for patent foramen ovale, and synthetic heart valves.

A stent can have virtually any structural pattern that is compatiblewith a bodily lumen in which it is implanted. Typically, a stent iscomposed of a pattern or network of circumferential and longitudinallyextending interconnecting structural elements or struts. In general, thestruts are arranged in patterns, which are designed to contact the lumenwalls of a vessel and to maintain vascular patency. A myriad of strutpatterns are known in the art for achieving particular design goals. Afew of the more important design characteristics of stents are radial orhoop strength, expansion ratio or coverage area, and longitudinalflexibility. The present invention is applicable to virtually any stentdesign and is, therefore, not limited to any particular stent design orpattern. One embodiment of a stent pattern may include cylindrical ringscomposed of struts. The cylindrical rings may be connected by connectingstruts.

A stent may be formed from a tube by laser cutting the pattern of strutsin the tube. The stent may also be formed by laser cutting a polymericsheet, rolling the pattern into the shape of the cylindrical stent, andproviding a longitudinal weld to form the stent. Other methods offorming stents are well known and include chemically etching a polymericsheet and rolling and then welding it to form the stent. A polymericwire may also be coiled to form the stent. The stent may be formed byinjection molding of a thermoplastic or reaction injection molding of athermoset polymeric material. Filaments of the compounded polymer may beextruded or melt spun. These filaments can then be cut, formed into ringelements, welded closed, corrugated to form crowns, and then the crownswelded together by heat or solvent to form the stent. Lastly, hoops orrings may be cut from tubing stock, the tube elements stamped to formcrowns, and the crowns connected by welding or laser fusion to form thestent.

Referring now in more detail to the exemplary drawings for purposes ofillustrating embodiments of the invention, wherein like referencenumerals designate corresponding or like elements among the severalviews, there is shown in FIG. 1 a cylindrically-shaped stent 10 withstruts 4 that form cylindrical rings 12 which are connected by linkingstruts 8. The cross-section of the struts in stent 10 isrectangular-shaped. The struts have abluminal faces 20, luminal faces22, and sidewall faces 26. The cross-section of struts is not limited towhat has been illustrated, and therefore, other cross-sectional shapesare applicable with embodiments of the present invention. The patternshould not be limited to what has been illustrated as other stentpatterns are easily applicable with embodiments of the presentinvention.

A stent can be made of a biostable and/or biodegradable polymer. Asindicated above, a stent made from a biodegradable polymer is intendedto remain in the body for a duration of time until its intended functionof, for example, maintaining vascular patency and/or drug delivery isaccomplished. After the process of degradation, erosion, absorption,and/or resorption has been completed, no portion of the biodegradablestent, or a biodegradable portion of the stent will remain.

It is generally desirable to minimize the interference of a stent ormarker with the structure of a lumen and/or with flow of bodily fluidthrough the lumen. Sharp edges, protrusions, etc. in the path of bloodflow can result in formation of turbulent and stagnant zones which canact as a nidus for thrombosis. A smaller and/or smoother profile of abody portion may be more hemocompatible. Additionally, a smaller andsmoother profile presented by a marker has much less likelihood ofcatching on other parts of the delivery system such as the guidewire orguiding catheter. The embodiments discussed herein involve markers,which after having been pressed into engagement onto a stent, do notcontribute significantly to the form factor, or profile, of the stent insuch a way that interferes with the structure of a lumen and/or withflow of bodily fluid through the lumen.

As indicated above, it is desirable to have the capability of obtainingimages of polymeric stents with x-ray fluoroscopy during and afterimplantation. Various embodiments of the present invention involvestents with markers disposed within depots or holes in a stent. A depotmay be formed in a structural element by laser machining. The depot mayextend partially or completely through the portion of the stent. Forexample, an opening of a depot may be on an abluminal or luminal surfaceand extend partially through the stent or completely through to anopposing surface. The markers may be sufficiently radiopaque for imagingthe stent.

FIG. 2 shows a stent pattern 40 with depots 44 for receiving a marker.In FIG. 2, the stent pattern 40 is shown in a flattened conditionshowing an abluminal or luminal surface so that the pattern can beclearly viewed. When the flattened portion of the stent pattern 40 is ina cylindrical condition, it forms a radially expandable stent. The stentpattern 40 includes cylindrically aligned structural elements 46 andlinking structural elements 48.

FIG. 3 shows a portion of a stent 60 with a depot 62 for retaining aradiopaque marker. The stent 60 includes cylindrically alignedstructural elements 64 and linking structural elements 66. The depot 62is located in a portion 68 which is a region of intersection of fourstructural elements. As depicted in FIG. 3, the depot 62 has acylindrical shape and extends completely through the radial thickness ofthe structural elements 64.

Certain embodiments of the present invention involve a deformedradiopaque marker disposed in a depot in a portion of the stent. Themarker may be coupled to the portion at least partially by aninterference or press fit between an expanded section of the marker andan internal surface of the portion of the stent within the depot. Insome embodiments, a marker in an undeformed state may be disposed in adepot and compressed to couple the marker within the depot. Compressingthe marker may expand a portion of the marker within the depot to createthe interference fit. Alternatively, the stent material may deform toachieve the interference fit with little or no deformation of themarker.

FIG. 4 shows a marker 70 disposed over the depot 62 extending through anabluminal surface 72 of the stent 60. In practice, the marker 70 may bepositioned using a syringe so that the marker rests on top of theabluminal surface 72, partially inside the depot 62, or both. The marker70 may be held at the end of the syringe by a vacuum or surface tensionof a viscous fluid.

The present invention encompasses markers fabricated by methodsincluding, but not limited to, molding, machining, assembly, or acombination thereof. All or part of a metallic or polymeric marker maybe fabricated in a mold or machined by a method such as laser machiningMarkers can have any shape or size. Preferably, though not necessarily,the markers are spherical in shape. Compared to markers of a cylindricalor other shape having a longitudinal axis, spherical markers are easierto align for placement on top of or into an opening formed in the stent.

Markers may be biodegradable. It may be desirable for the markers todegrade at the same or substantially the same rate as the stent. Forinstance, the markers may be configured to completely or almostcompletely erode at the same time or approximately the same time as thestent. Alternatively, the markers may degrade at a faster rate than thestent. In this case, the markers may completely or almost completelyerode before the body of the stent is completely eroded.

Also, a biocompatible biodegradable metal may be used for the markers. Abiocompatible biodegradable metal forms erosion products that do notnegatively impact bodily functions. The markers may be composed of apure or substantially pure biodegradable metal. Representative examplesof biodegradable metals for use in a marker may include, but are notlimited to, magnesium, zinc, and iron. Representative mixtures or alloysmay include magnesium/zinc, magnesium/iron, zinc/iron, andmagnesium/zinc/iron. Radiopaque compounds such as iodine salts, bismuthsalts, or barium salts may be compounded into the metallic biodegradablemarker to further enhance the radiopacity. Other representative examplesof biostable metals include platinum and gold.

Further, the markers may be a mixture of a biodegradable polymer and aradiopaque material. The radiopaque material may be biodegradable and/orbioabsorbable. Representative radiopaque materials may include, but arenot limited to, biodegradable metallic particles and particles ofbiodegradable metallic compounds such as biodegradable metallic oxides,biocompatible metallic salts, gadolinium salts, and iodinated contrastagents.

Certain embodiments of the present invention include disposing,coupling, or pressing radiopaque markers within a recess or depot in astent structure. Such embodiments are described below in connection withFIGS. 7-12.

FIGS. 5 and 6 show a stent 100 with markers 102 protruding radially fromthe stent 100. The markers 100 have been placed partially insiderecesses formed in the stent. The recesses are not shown for clarity andease of illustration. The recesses can be depots that extend completelythrough a stent structure, from an abluminal surface 104 to a luminalsurface 106. Alternatively, the recesses can be cavities that extendpartially into the stent structure. The terms “recess” and “opening” areused interchangeably herein. The stent has a central axis 108 extendingalong the entire length of the stent 100.

FIG. 7 shows a step mandrel 110 having a forward portion 112 and a rearportion 114. The forward portion 112 has a diameter 116 that is lessthan the diameter 118 of the rear portion 114. The forward portion isadapted to carry the stent 100. The mandrel 110 has a longitudinal axis119 extending along the entire length of the mandrel. The mandrel 110can be made of a relatively rigid material, in comparison to a stent,selected to provide firm support for the stent. Examples of suitablematerials includes plastics, such as Delrin, PVC, nylon, and others;metals such as steel, stainless steel, aluminum, titanium, and others;and glass. The mandrel 110 can also include a relatively resilient andcompliant material that is selected to provide sufficient support to thestent and to cushion the stent from excessive pressure from rollersdescribed below.

In FIG. 8, the stent 100 has been mounted onto the forward portion 112of the mandrel 110, which has been moved between two rollers 120 thatmay rotate about a retaining pin 122 in the direction of rotationalarrows 124. The forward portion 112 supports the stent 100 at itsluminal surface when the markers 102 are later pressed onto the stent.The rollers 120 have a circular cross-section. The retaining pin 122 issubstantially perpendicular to the central axis of the stent, whichallows each roller 120 to rotate about an axis that is substantiallyperpendicular to the longitudinal axis 119 of the stent 100. Furthermovement of the mandrel 110 and the stent 100 in the direction of axialarrow 126 will cause the markers 102 to be pressed into the surface ofthe stent 100 without damaging stent 100.

The rollers 120 can be made of a relatively rigid material, incomparison to the stent 100 and markers 102, to facilitate pressing themarkers into engagement with stent. Examples of suitable materialsincludes plastics, such as Delrin, PVC, nylon, and others; metals suchas steel, stainless steel, aluminum, titanium, and others; and glass.The rollers 120 can also include a relatively resilient and compliantmaterial that is selected to avoid damaging the stent 100 or markers 102yet provide sufficient pressure to press the markers into engagementwith the stent.

In some embodiments, the rollers 120 are positioned over the mandrel 110such that the top roller 120 does not contact stent 100 and contactsonly the markers 102. In this way, stress on the stent 100 is minimized.The bottom roller 120 contacts the stent to support the stent when thetop roller 120 presses the markers 120. The markers 102 are compactedtightly against the opening of stent 100 and the markers 102 areretained in the stent during stent crimping, delivery, and deployment ina bodily lumen.

FIG. 9 shows the stent 100 and mandrel 110 after having been movedaxially in the direction of axial arrow 126 from their positions in FIG.8. As a result, the markers 102 have been pressed into the openings ofstent 100 to fabricate a stent with markers that partially protrude fromthe stent 100. In one embodiment, the rollers 120 cause the markers 102to deform to reduce or eliminate protrusion of the markers 102 from thestent 100. Thus, the invention provides a method and apparatus forpressing markers into the stent such that the marker is tightly fit intothe stent, thereby improving marker retention onto the stent as well asreducing or eliminating protrusion of the marker from the stent.

Both markers 102 have been pressed into engagement with the stent 100with one continuous axial movement of the mandrel 110 carrying the stent100. FIG. 10 shows one of the markers 102 after having been pressed intoone of the openings 127 of the stent 100. Although only two markers 102are illustrated in FIGS. 8 and 9, it will be appreciated that any numberof markers may be positioned on the stent and pressed into engagementwith efficiency by one continuous axial movement of the mandrel 110. Useof the same set of rollers 120 on all the markers allows for uniformityin pressing the markers into engagement with the stent 100.

In other embodiments, the stent 100 may be passed through the gap 128between the rollers 120 in a plurality of discrete movements. In yetother embodiments, the stent 100 may be passed through the gap 128 morethan one time in order to press markers located at other portions of thestent. Also, the stent 100 may be passed through the gap 128 more thanone time to press the markers into engagement with the stent 100 in aprogressive fashion. For example, the gap 128 may be decreased aftereach time the stent 100 passes through the gap.

Referring again to FIG. 8, the gap 128 between the two rollers may beequal to or slightly larger than the outer diameter 130 of stent 100,thereby avoiding damage to the stent. The outer diameter 118 of the rearportion 114 of the mandrel 110 may be made equal to or substantiallyequal to the stent outer diameter 130. The outer diameter 118 may begreater than or equal to the stent outer diameter 130. Also, the outerdiameter 116 of the mandrel forward portion 112 may be equal to orsmaller than the inner diameter of the stent 100. In this way, the stent100 can have a slip or interference fit with the mandrel forward portion112.

The markers 102 are deformed by pushing the stent 100 through therollers 120. When the stent 100, having luminal surfaces supported bythe forward portion 112 of the mandrel 110, is pushed through therollers 120, the markers 102 are pressed inward and against the stent bythe rollers 120.

In practice, the free end 140 of the mandrel forward portion 112 may bepulled axially in the direction of axial arrow 126 until the markers 102are pressed by the rollers 120. In this manner, the mandrel rear portion114 engages a rear end 142 of the stent 100 so as to push the stent 100into the gap 128 between the rollers.

In some embodiments, the free end 144 of the mandrel rear portion 114may be pushed axially in the direction of axial arrow 126 until themarkers 102 are pressed by the rollers 120.

FIGS. 8 and 9 show how the stent 100 can be linearly translated relativeto the rollers 120. Linear translation of the stent 100 relative to therollers 120 can be achieved in other ways. For example, in otherembodiments, the stent 100 and the mandrel 110 are held fixed inposition while the rollers 120 are moved axially over the stent andmandrel until the markers 102 are pressed into engagement with thestent. In yet other embodiments, the mandrel 110 and rollers 120 areboth moved relative to each other to facilitate pressing the markers 102onto the stent 100.

It will be appreciated that any number of rollers may be used. Forexample, the mandrel 110 may be supported at one or both its ends suchthat the bottom roller 102 in FIGS. 8 and 9 can be eliminated, and onlythe top roller 120 in FIGS. 8 and 9 is needed to press the markers 102into engagement with the stent 100. More than two rollers, on the sameor different sides of the stent 100, may be used to provide greatersupport of the stent 100 or to guide the mandrel 110 into the gapbetween the rollers. Also, more than two rollers may be used to pressmarkers in a progressive fashion. For example, a first set of rollersmay be used to press the markers onto the stent, and a second set ofrollers that are spaced closer together may be used to press the markersfurther onto the stent. Progressive sets of rollers can have gapsbetween them that become smaller with each succeeding set of rollers.

FIG. 11 shows an apparatus and method in accordance with anotherembodiment of the present invention. A stent 150 is mounted over amandrel 152. A radiopaque marker 154 has been placed on the stent 150.Two rollers 156, adjacent the stent 150, are vertically aligned and areoriented such that a retaining pin 158 at the center of each roller issubstantially parallel to the central axis of the stent 150. In thisway, each of the rollers 156 may rotate along the direction ofrotational arrows 160 about a rotational axis that is substantiallyparallel to the central axis of the stent.

Instead of being moved axially as in FIG. 9, the stent 150 and themandrel 152 of FIG. 11 are moved laterally along the direction oflateral arrow 162 into a gap 164 between the rollers 156. The stent 150is oriented such that the marker 154 is pressed into engagement againstthe stent as the stent passes through the gap 164. The lateral directionof movement of the stent 150 is substantially perpendicular to thecentral axis of the stent 150. In other embodiments, the lateraldirection is at an angle between zero and ninety degrees from thecentral axis of the stent 150.

Preferably, the stent 150 is prevented from rotating about its centralaxis 168 while the stent passes through the gap 164. For example, thestent 150 may be held on the mandrel 152 with a slight interference fit,and the ends of the mandrel 152 may be secured against rotation. Also,the top roller 156 preferably rotates along the direction of arrow 160while the marker 154 passes beneath it to ensure that the marker ispressed downward onto the stent 150 and to avoid pushing the markersideways.

Referring again to FIG. 11, the gap 164 is carefully selected to allowthe stent 150 to pass through the gap 164 without being damaged.Preferably, the vertical size of the gap 164 is greater than or equal tothe outer diameter 166 of the stent 150. The vertical size of the gap164 is selected such that the rollers provide sufficient pressure todeform the marker 154 into engagement with an opening in the stent 154and to reduce the amount with which the marker 154 protrudes radiallyfrom the stent 154.

FIG. 12 shows an apparatus and method in accordance with yet anotherembodiment of the present invention. A stent 170 is mounted over amandrel 172. Three radiopaque makers 174 have been placed on the stent170. Two rollers 176, adjacent the stent 170, are each held by aretaining pin 178. The rollers 176 are vertically aligned and areoriented such that their rotational axes 177 are substantially parallelto the central axis 179 of the stent 170. In this way, the rollers 176may rotate along the direction of rotational arrows 180. The stent 170is placed between in the gap between the two rollers 176. The stent 170is oriented such that the markers 174 avoid contact with the rollerswhen first placed in the gap. Then, the stent 170 is rotated about itscentral axis along rotational arrow 182, thereby bringing the markers174 into contact with the rollers. As the stent 170 continues to rotate,the rollers 176 press the markers 174 into engagement with the stent.

FIG. 12 shows how the stent 170 can be rotationally translated relativeto the rollers 176. Rotational translation of the stent 170 relative tothe rollers 176 can be achieved in other ways. For example, in otherembodiments, the rollers 176 may rotate about the central axis 179 ofthe stent 170. After the stent 170 is placed between in the gap betweenthe two rollers 176, the rollers 176 are rotated about the central axis179 of the stent 170 while the stent 170 is prevented from rotatingabout its central axis 179, thereby bringing the rollers 176 intocontact with the markers 174. As the rollers 176 continue to rotate, therollers 176 press the markers 174 into engagement with the stent 170.Further, in other embodiments, both the stent 170 and the rollers 176are rotated about the central axis 179 of the stent 170.

Although three markers 174 are illustrated in FIG. 12, it will beappreciated that any number of markers may be positioned on the stentand pressed into engagement with efficiency by one continuous rotationalmovement of the stent 170. It will also be appreciated that additionalrollers may be used. Additional rollers may be used to provide greatersupport to the stent 170 or help keep the stent aligned within the gapbetween the rollers.

In FIGS. 8-12, the retaining pins at the center of the rollers are fixedin position relative to each other. In other embodiments, retaining pinsare movable relative to each other. For example, movable retaining pinsmay be held by a spring or device the biases the rollers to achieve anominal gap between the rollers. The nominal gap may be less than, equalto, or greater than the outer diameter of the stent. When the stent ispassed through the gap, the spring or other biasing device allows therollers to move apart so as to maintain a selected level of pressure onthe stent and marker. In this manner, the risk of damage to the stentand marker is reduced.

While several particular forms of the invention have been illustratedand described, it will also be apparent that various modifications canbe made without departing from the scope of the invention. It is alsocontemplated that various combinations or subcombinations of thespecific features and aspects of the disclosed embodiments can becombined with or substituted for one another in order to form varyingmodes of the invention. Accordingly, it is not intended that theinvention be limited, except as by the appended claims.

What is claimed is:
 1. A method of attaching a radiopaque marker onto a stent, the method comprising: providing a stent in an uncrimped state disposed over a mandrel, wherein the stent is biodegradable and is made of a biodegradable polymer; placing a spherical radiopaque marker at a recess in the stent in the uncrimped state; and rotating a roller about an axis substantially perpendicular to a central axis of the stent in the uncrimped state over the marker which presses the marker into the recess to attach the marker to the stent, wherein the pressing compresses the marker which expands a portion of the marker within the recess to create an interference fit between the expanded portion of the marker and biodegradable polymer of an internal surface of the recess.
 2. The method of claim 1, wherein the stent is translated along its central axis to the roller.
 3. The method of claim 1, wherein the radiopaque marker is deformed when it is pressed into the recess to reduce or eliminate protrusion of the marker from a stent surface.
 4. The method of claim 1, wherein the mandrel comprises a forward portion for carrying the stent, the forward portion having a diameter less than or equal to an inner diameter of the stent.
 5. The method of claim 1, wherein the mandrel comprises a rear portion having a diameter greater than or equal to an outer diameter of the stent. 